Microencapsulation of biocides and antifouling agents

ABSTRACT

The present invention relates to microencapsulated compositions of isothiazolone derivatives and other water insoluble biocides or antifouling agents. In particular, the present invention relates to microencapsulated 4,5 dichloro 2 n-octyl-3(2H)-isothiazolone(DCOIT), useful in marine antifouling coatings and paints.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Patent ApplicationNo. 60/609,741 filed Sep. 14, 2004.

FIELD OF THE INVENTION

The present invention relates to microencapsulated compositions ofisothiazolone derivatives useful as biocides or antifouling agents. Inparticular, the present invention relates to microencapsulated(4,5-dichloro-2-n-octyl-3(2H)-isothiazolone), and using themicrocapsules in marine antifouling coatings and paints.

BACKGROUND OF THE INVENTION

The present invention relates generally to the microencapsulation of(4,5-dichloro-2-n-octyl-3(2H)-isothiazolone (DCOIT), a biocide productavailable from Rohm and Haas Company and analogues and derivativesthereof. Marine coating and paint manufacturers customarily add biocidesto the paint to prevent or inhibit unwanted infestation of the films bymicroorganisms, e.g., fungi, such as molds and yeasts, and also bybacteria, algae, and cyanobacteria (so-called “soft fouling”) when thesepaints are applied on a vessel or underwater structure such as a pier.They have also been effective in some cases in preventing the growth ofbarnacles, tube worms, and the like (so-called “hard fouling”).

One biocide that has been investigated for use in marine paints andcoatings to prevent or control soft fouling and hard fouling is DCOIT.However, the solubility of DCOIT is low in seawater and high in xylene.These properties have led paint manufacturers desiring to add DCOIT tomarine paints to consider encapsulating DCOIT for incorporation intomarine paints. DCOIT microcapsules are known in the art but the capsulesreported in the literature to date have not been satisfactory. Forexample, xylene is a common solvent or base for marine paints. Unlessthe DCOIT capsules are essentially impermeable to xylene, the DCOIT mayleak out of the capsules and react with the paint binders. This maycause viscosity increases in certain paint formulations or the DCOIT maycause undesirable plasticizing of the paint film. If the microcapsule istoo permeable to water, the DCOIT may be leached away from the paintbinder shortly after the paint film is applied rendering the paintvulnerable to attack by microorganisms at too early a stage in itsservice life. Accordingly, there is a need for improved encapsulatedDCOIT compositions which provide in-can stability and yet graduallyrelease the DCOIT in the marine environment.

SUMMARY OF INVENTION

Because DCOIT is an oily material with very low solubility in water thatis liquid at temperatures at above about 40° C., certain embodiments ofthe invention utilize microencapsulation processes based uponoil-in-water emulsion systems.

In a further embodiment, the microcapsule shell or wall material isdesigned to be essentially impermeable to xlyene. This affords good“in-can” stability, and reduces the tendency for the DCOIT to leach fromthe capsules and interact with or plasticize the paint binders in thedried marine film. The microcapsule shell should also be permeable toseawater. To achieve a good release rate of the microencapsulated DCOIT,the shell materials should be inherently hydrophilic such that theygradually release DCOIT to the surface of the marine coating in thepresence of water and more particularly saltwater. In another embodimentof the invention, to enhance saltwater release, certain miscible organicsolvents having partial water solubility are encapsulated with theDCOIT, to enhance the rate with which DCOIT is released from the film inwater. In some embodiments, solvents such as dibasic esters, polyglycolsand glycol ether acetates, and isobutyl isobutyrate can be used to formmiscible DCOIT blends for encapsulation.

While the discussion herein addresses the encapsulation of DCOIT, thoseskilled in the art will recognize that other derivatives and analoguesof DCOIT and combinations thereof with other biocides could be processedherein in a similar manner. In particular, other hydrophobicisothiazolones having low water solubility (e.g., less than 2% and moreparticularly less than 1% in water at room temperature) such as 2n-octyl-3(2H)-isothiazolone (OIT) and benzisothiazolones (BIT) and theiralkyl derivatives can be encapsulated alone or in combination with oneanother or other biocides using the teachings herein.

DETAILED DESCRIPTION OF INVENTION

DCOIT can be encapsulated in a number of wall materials to providexylene in-can stability and to provide sustained release of the DCOITupon exposure to water (i.e., natural water or saltwater). In aparticular embodiment of the invention, the microcapsules are able tolimit the release of the encapsulated DCOIT to less than 10% andpreferably less than 5% in xylene at room temperature for 90 days. Inother embodiments, the xylene impermeability is such that less than 10%and preferably less than 5% of DCOIT is released at 45° C. over 90 days.

In accordance with an embodiment of the invention a microcapsule havinga wall formed from a hydrolyzed polyvinyl alcohol and phenolic resin isused for this purpose. In the case of microcapsules formed usingpartially hydrolyzed PVA, the hydrophilic character of the capsule shellcan be adjusted by varying the amount of partially hydrolyzed PVA thatis incorporated in the wall. In one embodiment, the partially hydrolyzedpolyvinyl alcohol and the phenolic resin components (e.g.,urea-rescorcinol-formaldehyde) are incorporated into the capsule shellin the amount of about 4 to about 8 parts by weight partially hydrolyzedPVA and about 20 to 30 parts phenolic resin. The encapsulation procedurefor making these microcapsules is well known in the art and isillustrated in Example 1 . As illustrated in this example, to preventthe DCOIT from reacting with the wall materials, the DCOIT is mixed witha solvent diluent such as a substituted aromatic solvent like SAS 310from Nisseki Chemical.

An amino-formaldehyde microcapsule (e.g. a melamine-formaldehyde (MF))shell provides very stable microcapsules impermeable to xylene, buttends to be too impermeable in seawater to provide good bio-efficacy foruse in conventional antifouling paints. It has been found that byoptimizing the shell thickness, a balance of the desired properties ofthe microcapsules can be achieved. In one embodiment of the presentinvention, control of microcapsule shell thickness by particle sizedistribution and shell-to-core ratios contributes diffusion performanceor sustained release characteristic. In one embodiment amicroencapsulated DCOIT based on an amino-urea-formaldehyde shellsystem, the target wall thickness is about 0.1 to about 0.2 micron, orthe shell to core ratio is about 0.03/1 to 0.05/1 by weight depending onthe mean capsule diameter and overall capsule size distribution profile.

Partially hydrolyzed PVA functions as a dopant in the amino-ureaformaldehyde wall. In accordance with one embodiment of the invention anagent referred to herein as a “dopant” is incorporated in themicrocapsule wall to enhance the ability of water to leach the DCOITfrom the capsule. According to one theory, the dopant interferes withthe amino-urea-formaldehyde condensation reaction and cause hydrophilicdefects in the microcapsule wall to facilitate the diffusion of theDCOIT. Representative examples of dopants include: partially and fullyhydrolyzed PVAs, hydroxylethylcellulose, hydroxypropylcellulose,methylcellulose, hydroxyethylmethylcellulose,hydroxypropylmethylcellulose, hyroxybutylmethylcellulose,ethylhydroxyethylcellulose and polyethylene glycols. While the amount ofdopant used will vary with the nature and thickness of the wall, in aparticular embodiment the dopants are incorporated into the wall in anamount of about 2 to about 10% by weight based upon the weight of thewall materials. For capsules having thick walls, the amount of requireddopant is expected to be more than the effective amount for thinner wallcapsules.

In order to enhance natural water or saltwater release or extraction ofthe DCOIT, in one embodiment of the invention, the DCOIT is mixed with apartially water miscible solvent. Examples of partial water misciblesolvents include esters and ethers and, more particularly, dibasicesters such as dimethyl adipate, or a blend of diisobutyl adipate,diisobutyl glutarate and diisobutyl succinate, polyglycol P-1200, andglycol ether EB acetate. Miscible organic solvents having partial watersolubility in the range of approximately 0.5 to 5% in water are used inone embodiment of the invention. The upper range on the water solubilityis not an absolute limit but reflects that if the solvent is more watersoluble, it may move into the continuous phase and not remain with theDCOIT to enhance its water leachability. High boiling hydrophilicsolvents, for example, having boiling points above 175° C. are desirableto use. If the boiling point of this solvent is too low, the solvent isdifficult to retain in the microcapsule during the capsule dryingoperation. In a particular embodiment the higher boiling partially watermiscible solvent is incorporated into the core in an amount of about 5to about 50% and in other embodiments in an amount of about 10 to 25% byweight based upon the weight of the DCOIT.

In some embodiments a dual walled capsule has been used. In particular adual encapsulation process with a first interfacial capsule wall ofacrylic polymer and second wall of PVA-urea-resorcinol-gluteraldehydecan be used as illustrated in more detail in Example 3 . The dualacrylic-PVA-URG system is advantageous because it provides aformaldehyde free product. Encapsulation based on PVA-URG or acrylicalone typically results in quite leaky capsules that are difficult torecover as a powder. However, combining the two systems to form hybridcapsule shells has resulted in dry free flow capsule powders.

Another embodiment of the present invention, uses a dual encapsulationprocess with a first interfacial capsule wall of acrylic polymer andPVA-urea-resorcinol-formaldehyde(URF) polymer is illustrated in Example4 . In still another embodiment of the present invention, dual wallmicrocapsules are formed comprising a first wall that is an interfacialreaction product of an aromatic polyisocyanate, a second wall ofPVA-urea-resorcinol-formaldehyde(URF) condensation polymer isillustrated in Example 5 . Other microcapsule wall systems that can beused in other embodiments of the present invention, include an MF shellcapsule further re-encapsulated with PVA-URF (Example 6); an MF shellcapsules re-encapsulated with PVA-urea-resorcinol-gluteraldehyde polymer(Example 7); a PVA-URF shell capsule re-encapsulated with an MF process;a hydrophilic shell comprising gelatin-gum arabic as a first shell and aovercoat of melamine-formaldehyde resin or aurea-resorcinol-formaldehyde condensation polymer (Examples 8 and 9).

Regarding the dual wall systems, the MF provides significant improvementin xylene stability while the PVA-URF or PVA-URG wall providesadditional hydrophilicity in the shell to facilitate diffusion of theDCOIT in an aqueous environment. The dual wall system provides shellstrength to minimize capsule damage during paint formulation and sprayapplication to ship hulls. The ultimate shell characteristics formicroencapsulated DCOIT are achieved by adjusting the thickness of thetwo wall materials to afford a balance of xylene stability and diffusionof DCOIT in seawater.

In another embodiment of the invention, the DCOIT is first encapsulatedin a thin (e.g., less than about 0.1 micron) MF wall, and then furtherencapsulated in a PVA wall as described above. In this case the use ofthe solvent diluent like the SAS 310 may not be necessary for theencapsulation using the PVA-URF system since the MF wall prevents theDCOIT from reacting with the wall components. Thus, this dualencapsulation process allows the DCOIT to be encapsulated without thediluting effect of solvent and therefore affords a more cost effectiveproduct. Of course, the partially water miscible solvent may continue tobe used with the DCOIT to enhance water leachability.

In one embodiment of the present invention, multi-shell microcapsulescomprising an interfacial first wall with the reaction of an aromaticpolyisocyanate, a second shell of gelatin-gum arabic and a thirdovercoat capsule wall of melamine-formaldehyde resin (Example 10). The3-wall system of isocyanate/gelatin-gum arabic/MF is just another methodof controlling capsule-wall permeability in an aqueous environment. Theisocyanate-gelatin interface reduces premature diffusion of the DCOIT inthe xylene-based paints. The interfacial reaction of polyisocyanate inconjunction with the PVA-URF provides another method ofmicroencapsulating DCOIT. The interfacial skin of polyurethane orpolyurea formed by the reaction of the isocyanate with the PVA or apolyamine provides an additional barrier for improving capsule stabilityin the xylene based MAF paints.

In accordance with one embodiment of the invention, the microcapsulesshould be small in order to be used in spray applications and to providebetter distribution of the active ingredient in the paint film. In oneembodiment, the capsule size range is about 5 microns to about 40microns, and more typically about 5 microns to about 20 microns.Distribution of the biocide improves with smaller capsules such as lessthan 10 microns.

The microcapsules are usually dried before incorporating them into thepaint formulation. Any conventional process for drying microcapsulesincluding spray drying can be used for this purpose. However, forcertain water-based paints, it will in some cases be possible toincorporate the microcapsules into the paint without drying.

In accordance with an embodiment of this invention, the encapsulatedbiocide is combined with a film former or binder such as the filmformers and binders that have been proposed for use in marine paints,gel coats and the like (e.g., natural or synthetic resin or rosinbinders) to provide coating compositions. In one embodiment of theinvention, marine antifouling paint compositions can be prepared. Suchpaints can be prepared by incorporating the microcapsules describedherein into the paint in an amount that is sufficient to impart thedesired antifouling properties. Such amounts can be readily determinedempirically by those skilled in the art. Examples of marine paintsreported in the literature that are useful herein may contain about 5 to50% by weight, or in other cases about 10 to 25% by weight, xylene oranother solvent base, about 20 to 30% by weight zinc resinate toplasticize the resin binder, about 10 to 20% by weight resin binder,about 0 to 50%, or in other cases about 30 to 40% by weight, cuprousoxide pigment, and 4 to 6% by weight thixotropic viscosity modifier.Generally, the ingredients were thoroughly mixed as follows: 200 ml ofthe paint composition is introduced into a tight metallic container of0.5 L capacity together with 100 ml (bulk volume) of glass beads with adiameter of 2-3 mm. The container is then shaken for 45 minutes on amechanical shaker. The final paint composition is separated from theglass beads by filtration. The microencapsulated DCOIT biocide isincorporated in the paint in an amount to provide the marine antifoulingproperties that are desired (e.g., about 3 to 10% by weight). The amountrequired will be a function of the rate at which the DCOIT is leachedfrom the microcapsules. In one embodiment, the capsules are added in anamount to provide about 2% DCOIT in the dry film.

Other applications for microencapsulated DCOIT may include use as acontrolled release biocide in latex or oil-based paints and coatings,adhesives, sealants, caulks, mastic and patching materials, buildingmaterials, roofing materials such as shingles, plastics, polymercomposites, paper processing, paper coatings, wood preservation, coolingwater towers, metal working fluids, and as a general preservative.Additionally, while the discussion herein particularly addresses xylenebased paints, the encapsulation techniques described herein may also beuseful in providing solvent resistance and in-can stability for paintsbased on other solvents such asC-3 to C-10 ketones, more specificallyC-5 to C-7 ketones (e.g., methyl isobutyl ketone (MIBK), isoamyl methylketone, hexanone, etc.); C-1 to C-10 alcohols, more specifically C-4 toC-6 alcohols (e.g., n-butanol and 2-butoxy ethanol); C-5 to C-50aliphatic and aromatic hydrocarbons, more specifically C5-C32hydrocarbons and still more specifically C5-C19 hydrocarbons (e.g.,petroleum spirits, ethyl benzene, and trimethyl benzene); and for paintscontaining plasticizers such as phosphate esters and aromatic esters.

In accordance with another embodiment of the invention, a combination oftwo or more microcapsules can be used which release the biocide atdifferent rates, for example, one microcapsule may be used that releasesthe biocide after or over a short time period and anothermicrocapsule(s) might be used that releases the biocide after or over asomewhat longer time. These microcapsules may be made of different wallmaterials or different wall thicknesses in accordance with otherembodiments of the invention.

The present invention is further illustrated by the followingnon-limiting examples.

EXAMPLE 1 Microencapsulation of Kathon 287T Biocide Containing SolventDiluent

An aqueous phase was prepared consisting of 160 grams each of a 5%strength aqueous solutions of polyvinyl alcohol, Vinol 540 and Vinol 125(both manufactured by Air Products) and 300 grams of water. The aqueousphase is heated to 40° C.

The core material is prepared as a mixture of 100 grams of Kathon 287T(97%) manufactured by Rohm and Haas and 100 grams of a substitutedaromatic solvent, SAS 310 manufactured by Nisseki Chemical and heated to40° C. The aqueous phase and the core material are added to a 1-quartWaring Blender jar and the slurry is emulsified at moderate speed forabout 15 minutes to produce an oil-in-water emulsion of droplets in thesize range of about 10 to 40 microns. The emulsion is transferred to a1-liter beaker. The slurry is slowly agitated using a turbine impellorwhile maintaining the temperature at about 40° C. A solution of 4 gramsof urea and 10 grams of resorcinol in 60 grams of water is slowly addedto the emulsion. A solution of 2 grams sodium sulfate in 30 grams ofwater is subsequently added to the slurry in drop-wise fashion. A 30 ml37% formaldehyde solution is added drop-wise followed 10 minutes laterby the addition of 20 ml of a 10% sulfuric acid solution over a 5-minuteperiod. The slurry is warmed to 45° C. and after about one hour asolution of 4 g of urea, 6 g of resorcinol, 50 g of water and 20 ml of37% formaldehyde second addition is added drop-wise. This solution maybe divided, with half added in 15 minutes followed by a 15-minute holdperiod prior to adding the second half. One hour later another solutionlike the proceeding is added to the slurry in the same fashion. Theslurry is heated to 55° C. and allowed to stir for 16 hours. Themicrocapsule slurry is cooled to ambient temperature and pH adjusted to7.0 using 10% sodium hydroxide solution. The slurry is then diluted withwater and strained using a 125-150 um sieve to remove encapsulated airand any debris. The slurry is set aside to allow the microcapsules tosettle. The supernatant liquid is decanted and microcapsule concentrateis re-slurried with water. A small amount of Syloid 244 silica from W.R. Grace Company is stirred into the slurry; and the microcapsules arevacuum-filtered using Whatman 4.0 paper and tray dried to produce 230grams of dry free-flowing powder. The resultant microcapsules are mostly10-40 microns and can be incorporated in a marine coating composition toimpart anti-fouling properties. The microcapsules were tested forstability in xlyene by placing a 50-mg sample into 50 mls of xlyene andperiodically analyzing a small aliquot of the xylenespectrophotometrically for the presence of DCOIT to determine the amountdiffused through the capsule shell. Samples were tested after roomstorage. 1.1% DCOIT was released after 56 days at room temperature.

EXAMPLE 2 Microencapsulation of Neat Kathon 287T Biocide

The microencapsulation of the neat Kathon 287T is carried out in anaqueous continuous phase to produce microcapules comprising anamino-formaldehyde shell. An aqueous phase is prepared consisting of27.5 g of a 3.75% ethylene maleic anhyride co-polymer (manufactured byZeeland Chemical Company) solution and 30.37 g of water and heated to45° C. In a separate vessel, 32.5 g of Kathon 287T 97% manufactured byRohm and Haas and is heated to 45° to form a liquid melt. An emulsion isprepared by dispersing the melted Kathon core material in the aqueousphase using an Ika-Works mixer and high speed turbine with the speedcontrolled to produce Kathon droplets mostly in the range of 10-50 um.While maintaining the temperature at 45° C. during the emulsificationprocess, 5.58 grams of Cymel 385 manufactured by Cytec is added tostabilize the emulsion. After about 15 minutes, the agitation speed isreduced and additional 1.79 grams of the Cymel 385 resin is added whilemaintaining the temperature at around 50° C. After a few minutes, a5-gram solution of a 5% polyvinyl alcohol Vinyl 540 manufactured by AirProducts is added followed a drop-wise addition of 11 grams of a 15%salt solution of potassium dihydrogen phosphate over a 10 minute period.The temperature of the microcapsule slurry is slowly increased to 65° C.and 2.06 grams of urea is added about 1.5 hours after the salt addition.After an additional 4 hours of stirring at 65° C., the slurry is cooledto ambient and the ph adjusted to 7.0 using 45% potassium hydroxidesolution. The slurry is diluted 1:1 with water and sieved using a 125 umsieve to remove encapsulated air and any debris. The microcapsules areallowed settle and the supernatant liquid decanted. The microcapsuleconcentrate is re-slurried in water and the decantation processrepeated. The microcapsules are re-slurried with water; vacuum filteredusing Whatman 4.0 paper; and tray dried either on the lab bench atambient conditions or in a warm oven. The resultant microcapsules are adry-free flowing powder that can be readily incorporated into a marinepaint formulation to provide a marine coating in accordance with oneembodiment of the invention. The microcapsules were tested using thexylene extraction test described in Example 1 and 1.4% DCOIT wasreleased after 56 days at room temperature.

EXAMPLE 3A Microencapsulation of DCOIT Biocide with a Dual Shell ofAcrylic and PVA-urea-resorcinol-gluteraldehyde

An internal phase is prepared by mixing together molten Kathon 287T (150g) at a temperature of around 50° C., with methyl methacrylate (10 g) 1,4, butanediol diacrylate (10 g) and trimethylolpropane trimethacrylate(10 g). Just prior to emulsification, tertbutyl perpivalate (1 g) ismixed in to the internal phase. The internal phase is homogenized intowater (254 g) containing polyvinyl alcohol (Elvanol 50-42) (6 g) using aWaring 1 liter blender for 10 minutes until a stable emulsion is formed.The emulsion is then transferred into a 1-liter beaker with overheadstirring, thermometer and nitrogen supply and deoxygenated with nitrogenfor 1 hour while heating to 90° C. The batch is then held at 90° C. for1.5 hours after nitrogen removal before being cooled down to 45° C. Theresulting emulsion contains polymeric particles each comprising apolymeric shell encapsulating the Kathon 287T having a mean particlesize of 19 microns.

The particles of encapsulated Kathon 287T are then subjected to asecondary treatment at 45° C. involving drop wise additions of aluminumsulfate TG 8.3% (60 g) over 12 minutes, 10 v/v % sulfuric acid (34 g)over 12 minutes, and a mixture of urea (2 g), resorcinol (1.5 g), andwater (20 g) over 12 minutes. Then a mixture of 25% gluteraldehyde (5 g)and water (5 g) are added drop wise very slowly over 20 minutes toprevent aggregation. Then a second addition of urea (2 g), resorcinol(1.5 g), and water (20 g) is added over 12 minutes followed by a mixtureof 25% gluteraldehyde (5 g) and water (5 g) added drop wise over 12minutes. Followed by a third addition of urea (2 g), resorcinol (1.5 g),and water (20 g) is added over 12 minutes followed by a mixture of 25%gluteraldehyde (5 g) and water (5 g) added drop wise over 12 minutes.After all additions are made the temperature is increased from 45° C. to50° C. and held overnight to cure for approximately 16 hours. Aftercooling and pH neutralization the microcapsules are filtered and driedto produce a fine free flowing powder that can be readily incorporatedinto a marine paint formulation to provide a marine coating inaccordance with one embodiment of the invention.

EXAMPLE 3B

Example 3A is repeated using a solution of sodium sulfate powder (2 g)dissolved in water (30 g) instead of aluminum sulfate. The sodiumsulfate solution is added drop wise over 12 minutes. Again, a dry freeflowing powder was achieved that can be readily incorporated into amarine paint formulation to provide a marine coating in accordance withone embodiment of the invention.

EXAMPLE 4 Dual Encapsulation Process with a First Interfacial CapsuleWall of Acrylic Polymer and PVA-urea-resorcinol-formaldehyde Polymer

An internal phase is prepared by mixing together molten Kathon 287T (150g) at a temperature of around 50° C., with methyl methacrylate (10 g) 1,4, butanediol diacrylate (10 g) and trimethylolpropane trimethacrylate(10 g). Just prior to emulsification, tertbutyl perpivalate (1 g) ismixed in to the internal phase. The internal phase is homogenized intowater (453 g) containing polyvinyl alcohol (Elvanol 50-42) (6 g) and(Elvanol 71-30) (6 g) using a Waring 1 liter blender for 8 minutes untila stable emulsion is formed. The emulsion is then transferred into a1.5-liter beaker with overhead stirring, thermometer and nitrogen supplyand deoxygenated with nitrogen for 1 hour while heating to 90° C. Thebatch is then held at 90° C. for 1.5 hours after nitrogen removal beforebeing cooled down to 40° C. The resulting emulsion contains polymericparticles each comprising a polymeric shell encapsulating the Kathon287T having a mean particle size of 19 microns. The particles ofencapsulated Kathon 287T are then subjected to a secondary treatment at40° C. involving drop wise addition of a mixture of urea (3 g),resorcinol (7.5 g), and water (45 g) over 12 minutes. Then a solution ofsodium sulfate powder (1.5 g) and water (22.5 g) is added drop wise over10 minutes. Then a 37% solution of formaldehyde (22.5 ml) is added dropwise over 10 minutes. After a 10-minute hold at 40° C., 10 v/v %sulfuric acid is added drop wise over 6 minutes. The batch is thenstirred and slowly heated to 45° C. over 1 hour. Then a second additionof a solution of urea (3 g), resorcinol (4.5 g), water (37.5 g) and 37%formaldehyde (15 ml) is divided in half and added over 12 minutesfollowed by the second half after a 15 minute hold at 45° C. The batchis then stirred and slowly heated to 48° C. over 1 hour. A thirdaddition of urea (3 g), resorcinol (4.5 g), water (37.5 g) and 37%formaldehyde (15 ml) is added over 12 minutes. After all additions aremade the temperature is increased from 48° C. to 50° C. and heldovernight to cure for approximately 16 hours. After cooling and pHneutralization the microcapsules are filtered and dried to produce a dryproduct that can be readily incorporated into a marine paint formulationto provide a marine coating in accordance with one embodiment of theinvention.

EXAMPLE 5 Dual Wall Microcapsules Comprising an Interfacial First Wallwith the Reaction of an Aromatic Polyisocyanate, a Second Shell ofPVA-urea-resorcinol-formaldehyde Condensation Polymer

An internal phase is prepared by mixing together molten Kathon 287T (90g) at a temperature of around 50° C., with Desmodur L 75 (Bayer) (10 g).The internal phase is homogenized into water (302 g) containingpolyvinyl alcohol (Elvanol 50-42) (4 g) and (Elvanol 71-30) (4 g) usinga Waring 1 liter blender for 13 minutes until a stable emulsion isformed. The emulsion is then transferred into a 1-liter beaker withoverhead stirring and thermometer. The batch is then heated to 50° C.and a solution of triethylene diamine (0.5 g) and water (10 g) is addeddrop wise. The batch is then held at 50° C. overnight. The resultingemulsion contains polymeric particles each comprising a polymeric polyurea shell encapsulating the Kathon 287T having a mean particle size of16 microns. The particles of encapsulated Kathon 287T are then subjectedto a secondary treatment at 40° C. involving drop wise addition of amixture of urea (2 g), resorcinol (5 g), and water (30 g) over 12minutes. Then a solution of sodium sulfate powder (1 g) and water (15 g)is added drop wise over 6 minutes. Then a 37% solution of formaldehyde(15 ml) is added drop wise over 7 minutes. After a 10-minute hold at 40°C., 10 v/v % sulfuric acid is added drop wise over 5 minutes. The batchis then stirred and slowly heated to 45° C. over 1 hour. Then a secondaddition of a solution of urea (2 g), resorcinol (3 g), water (25 g) and37% formaldehyde (10 ml) is divided in half and added over 12 minutesfollowed by the second half after a 15 minute hold at 45° C. The batchis then stirred and slowly heated to 48° C. over 1 hour. A thirdaddition of urea (2 g), resorcinol (3 g), water (25 g) and 37%formaldehyde (10 ml) is added over 12 minutes. After all additions aremade the temperature is increased from 48° C. to 50° C. and heldovernight to cure for approximately 16 hours. After cooling and pHneutralization the microcapsules are filtered and dried to produce alumpy isolation.

EXAMPLE 6 MF Shell Capsules Re-Encapsulated with PVA-URF Polymer

An internal phase is prepared by melting Kathon 287T (260 g) at atemperature of around 50° C. The internal phase is homogenized into anaqueous A Solution consisting of 110.0 g of a 3.75% ethylene maleicanhydride copolymer solution and 121.48 g of water using a Waring 1liter blender. While maintaining the temperature of around 50° C. duringthe emulsification process, Cymel 385 (22.33 g) manufactured by Cytec isadded to stabilize the emulsion. After about 15 minutes, the agitationis reduced and 10-50 um droplets are formed. The emulsion is thentransferred into a 1-liter beaker with overhead stirring andthermometer. Then a 15% salt solution (44 g) of potassium dihydrogenphosphate is added drop wise. The batch is then heated to 65° C. over1.5 hours and held for 4 hour then cooled. The resulting emulsioncontains polymeric particles each comprising a polymericamino-formaldehyde shell encapsulating the Kathon 287T having a meanparticle size of 16 microns.

The particles of encapsulated Kathon 287T slurry are then divided inhalf. This (272 g) fraction is subjected to a secondary treatment at 45°C. involving drop wise addition of a mixture of urea (3 g), resorcinol(3 g), and water (30 g) over 10 minutes. Then a 37% solution offormaldehyde (18 ml) is added drop wise over 7 minutes. After a10-minute hold at 45° C., 10 v/v % sulfuric acid (10 ml) is added dropwise over 5 minutes. The batch is then stirred at 45° C. over 1 hour.Then a second addition of a solution of urea (3 g), resorcinol (7 g),water (30 g) and 37% formaldehyde (25 ml) is divided in half and addedover 12 minutes followed by the second half after a 15 minute hold at45° C. The batch is then stirred and slowly heated to 55° C. over 1hour. Then heated to 60° C. for 3 hours and cooled. After cooling and pHneutralization the microcapsules are filtered and dried to produce afine free flowing powder that can be readily incorporated into a marinepaint formulation to provide a marine coating in accordance with oneembodiment of the invention. The microcapsules were tested using thexylene extraction test described in Example 1 except that a sample ofthe microcapsules was also tested at 45° C. In this test 0.4% DCOIT wasreleased after 28 days at room temperature and 2.7% DCOIT was releasedafter 28 days at 45° C.

EXAMPLE 7A MF Shell Capsules Re-Encapsulated withPVA-urea-resorcinol-gluteraldehyde Polymer

An internal phase is prepared by melting Kathon 287T (260 g) at atemperature of around 50° C. The internal phase is homogenized into anaqueous solution consisting of 110.0 g of a 3.75% ethylene maleicanhydride copolymer solution and 121.48 g of water using a Waring 1liter blender. While maintaining the temperature of around 50° C. duringthe emulsification process, Cymel 385 (22.33 g) manufactured by Cytec isadded to stabilize the emulsion. After about 15 minutes, the agitationis reduced and 10-50 um droplets are formed. The emulsion is thentransferred into a 1-liter beaker with overhead stirring andthermometer. Then a 15% salt solution (44 g) of potassium dihydrogenphosphate is added drop wise. The batch is then heated to 65° C. over1.5 hours and held for 4 hour then cooled. The resulting emulsioncontains polymeric particles each comprising a polymericamino-formaldehyde shell encapsulating the Kathon 287T having a meanparticle size of 16 microns. The particles of encapsulated Kathon 287Tslurry are then divided and half are filtered to a wet cake of 80.51%(127.5 g dry wt.). The wet cake is then re-suspended in a mixture ofwater (254 g) containing polyvinyl alcohol (Elvanol 50-42) (6 g) andsubjected to a secondary treatment at 45° C. involving drop wiseadditions of aluminum sulfate TG 8.3% (60g) over 12 minutes, 10 v/v %sulfuric acid (34 g) over 12 minutes, and a mixture of urea (2 g),resorcinol (1.5 g), and water (20 g) over 12 minutes. Then a mixture of25% gluteraldehyde (5 g) and water (5 g) are added drop wise very slowlyover 20 minutes to prevent aggregation. Then a second addition of urea(2 g), resorcinol (1.5 g), and water (20 g) is added over 12 minutesfollowed by a mixture of 25% gluteraldehyde (5 g) and water (5 g) addeddrop wise over 12 minutes. Followed by a third addition of urea (2 g),resorcinol (1.5 g), and water (20 g) is added over 12 minutes followedby a mixture of 25% gluteraldehyde (5 g) and water (5 g) added drop wiseover 12 minutes. After all additions are made the temperature isincreased from 45° C. to 50° C. and held overnight to cure forapproximately 16 hours. After cooling and pH neutralization themicrocapsules are filtered and dried to produce a fine free flowingpowder that can be readily incorporated into a marine paint formulationto provide a marine coating in accordance with one embodiment of theinvention. The microcapsules were tested using the xylene extractiontest described in Example 1 except that a sample of the microcapsuleswas also tested at 45° C. In this test 2.4% DCOIT was released after 14days at room temperature and 3% DCOIT was released after 14 days at 45°C.

EXAMPLE 7B

Example 7A is repeated using a solution of sodium sulfate powder (2 g)dissolved in water (30 g) instead of aluminum sulfate. The sodiumsulfate solution is added drop wise over 12 minutes. Again, a dry freeflowing powder was produced that can be readily incorporated into amarine paint formulation to provide a marine coating in accordance withone embodiment of the invention.

EXAMPLE 8 Dual Encapsulation with Gelatin/Gum Arabic as the First Shelland Melamine Resin as the Second Wall

In a 1000 ml beaker fitted with an Ika-Works mixer and 4-blade turbineimpellor, dissolve 6 grams 300 bloom gelatin and 6 grams spray dried gumarabic in 240 ml deionized water. Start mixing at room temperature,again and heat to 80° C. with stirring.

Adjust the pH to clear the solution with 10% NaOH (˜pH 7). Adjust the pHto 4.1 with 10% Acetic Acid. Warm 40 grams Kathon 287T to 50-60° C. tomelt. Transfer the Gelatin/Gum Arabic solution to a warm blender jar andadd the Kathon 287T melt. Emulsify slowly (˜10 min) to achieve thedesired droplet size (10-40 microns). Transfer back to the beaker-mixerapparatus in an empty water bath. Using a separatory funnel, about 175ml warm (50-60° C.) deionized water was added drop-wise. Check with amicroscope to observe liquid-liquid phase separation of a fluid phasethat partially wraps the droplets. Adjust the amount of deionized waterup or down to achieve this result. Begin slow cooling the beaker byadding a few ice cubes to the water bath. At 35° C., the fluid polymerphase should be observed microscopically. Continue slow cooling to 28°C. Check microscopically again to verify if the solution is mostly clearwith a noticeable wall formation and little free polymer. Continue slowcooling to 25° C. One should observe a substantial wall and no freepolymer. Continue cooling to 15° C., at which time 10 grams of 25%gluteraldehyde is added. After adding more ice, stir overnight, allowingthe reaction to warm to room temperature. Decant 2 times by lettingcapsules settle and rinsing with 300 ml deionized water. Capsules can beisolated at this point by filtering and adding 1.5 grams Aerosil 972R tothe filter-cake and shaking in a wide-mouth bottle to mix well. Thepowder is laid out on a paper towel to bench-dry overnight. Thisresulted in a free flowing powder with single (droplet) capsules as wellas some aggregates.

A second wall can be added by filtering the twice-decanted slurry. Thewet filter-cake is re-suspended in 25 grams of 3.75% EMA solution and 50ml deionized water. Begin heating to 50° C. and while dripping in 3grams Cymel 385 in 12 ml deionized water. At 50° C., drop-wise, add 10grams 15% dihydrogen phosphate solution. Heat to 65° C. and hold overnight. Cool to room temperature and adjust the pH to 7.0 with 45%Potassium Hydroxide solution. Filter, and wash with deionized water.Spread out on a paper towel to dry. This resulted in a free flowingpowder with single (droplet) capsules as well as some aggregates.

EXAMPLE 9 Dual Encapsulation with Gelatin/Gum Arabic as the First Shelland Urea-resorcinol-formaldehyde Polycondensate as the Second Wall

In a 1000 ml beaker fitted with an Ika-Works mixer and 4-blade turbineimpellor, dissolve 6 grams 300 bloom gelatin and 6 grams spray dried gumarabic in 240 ml deionized water. Start mixing at room temperature,again and heat to 80° C. with stirring.

Adjust the pH to clear the solution with 10% NaOH (˜pH 7). Adjust the pHto 4.1 with 10% Acetic Acid. Warm 40 grams Kathon 287T to 50-60° C. tomelt. Transfer the Gelatin/Gum Arabic solution to a warm blender jar andadd the Kathon 287T melt. Emulsify slowly (˜10 min) to achieve thedesired droplet size (10-40 microns). Transfer back to the beaker-mixerapparatus in an empty water bath. Using a separatory funnel, about 175ml warm (50-60° C.) deionized water was added drop-wise. Check with amicroscope to observe liquid-liquid phase separation of a fluid phasethat partially wraps the droplets. Adjust the amount of deionized waterup or down to achieve this result. Begin slow cooling the beaker byadding a few ice cubes to the water bath. At 35° C., the fluid polymerphase should be observed microscopically. Continue slow cooling to 28°C. Check microscopically again to verify if the solution is mostly clearwith a noticeable wall formation and little free polymer. Continue slowcooling to 25°. One should observe a substantial wall and no freepolymer. Continue cooling to 15° C., at which time 10 grams of 25%gluteraldehyde is added. After adding more ice, stir overnight, allowingthe reaction to warm to room temperature. Decant 2 times by lettingcapsules settle and rinsing with 300 ml deionized water. Capsules can beisolated at this point by filtering and adding 1.5 grams Aerosil 972R tothe filter-cake and shaking in a wide-mouth bottle to mix well. Thepowder is laid out on a paper towel to bench-dry overnight. Thisresulted in a free flowing powder with single (droplet) capsules as wellas some aggregates. A second wall can be added by filtering thetwice-decanted slurry. The wet filter-cake is re-suspended in 25 gramsof 3.75% EMA solution and 50 ml deionized water. Begin heating to 50° C.and while dripping in 2 grams Urea and 0.2 grams resorcinol in 10 mldeionized water. At 50° C., drop-wise, add 5 grams 37% Formaldehydesolution then 10 grams 15% dihydrogen phosphate solution. Heat to 55° C.and hold over night. Cool to room temperature and adjust the pH to 7.0with 45% Potassium Hydroxide solution. Filter, and wash with deionizedwater. Spread out on a paper towel to dry. This resulted in a freeflowing powder with single (droplet) capsules as well as someaggregates.

EXAMPLE 10 Multi-shell Microcapsules Comprising polyurethane/polyurea,Gelatin/Gum Arabic and Melamine Resin

In a 1000 ml beaker fitted with an Ika-Works mixer and 4-blade turbineimpellor, dissolve 6 grams 300 bloom gelatin and 6 grams spray dried gumarabic in 240 ml deionized water. Start mixing at room temperature,again and heat to 80° C. with stirring.

Adjust the pH to clear the solution with 10% NaOH (˜pH 7). Adjust the pHto 4.1 with 10% Acetic Acid. Warm 40 grams Kathon 287T to 50-60° C. tomelt. Add 4 grams Desmondure CB-75 and mix well. Transfer theGelatin/Gum Arabic solution to a warm blender jar and add the Kathon287T solution. Emulsify slowly (˜10 min) to achieve the desired dropletsize (10-40 microns). Transfer back to the beaker-mixer apparatus in anempty water bath. Using a separatory funnel, about 175 ml warm (50-60°C.) deionized water was added drop-wise. Check with a microscope toobserve liquid-liquid phase separation of a fluid phase that partiallywraps the droplets. Adjust the amount of deionized water up or down toachieve this result. Begin slow cooling the beaker by adding a few icecubes to the water bath. At 35° C., the fluid polymer phase should beobserved microscopically. Continue slow cooling to 28° C. Checkmicroscopically again to verify if the solution is mostly clear with anoticeable wall formation and little free polymer. Continue slow coolingto 25° C. One should observe a substantial wall and no free polymer.Continue cooling to 15° C., at which time 10 grams of 25% gluteraldehydeis added. After adding more ice, stir overnight, allowing the reactionto warm to room temperature. Decant 2 times by letting capsules settleand rinsing with 300 ml deionized water. Capsules can be isolated atthis point by filtering and adding 1.5 grams Aerosil 972R to thefilter-cake and shaking in a wide-mouth bottle to mix well. The powderis laid out on a paper towel to bench-dry overnight. This resulted in afree flowing powder with single (droplet) capsules as well as someaggregates. A third wall can be added by filtering the twice-decantedslurry. The wet filter-cake is re-suspended in 25 grams of 3.75% EMAsolution and 50 ml deionized water. Begin heating to 50° C. and whiledripping in 3 grams Cymel 385 in 12 ml deionized water. At 50° C.,drop-wise, add 10 grams 15% dihydrogen phosphate solution. Heat to 65°C. and hold over night. Cool to room temperature and adjust the pH to7.0 with 45% Potassium Hydroxide solution. Filter, and wash withdeionized water. Spread out on a paper towel to dry. This resulted in afree flowing powder with single (droplet) capsules as well as someaggregates.

Having described the invention in detail and with reference to specificadvantages thereof it will be apparent that numerous modifications arepossible without departing from the spirit and scope of the followingclaims.

1. A microencapsulated biocide comprising an isothiazolone biocide orantifouling agent as a core material encapsulated in a wall materialthat has a xylene impermeability such that less than 10% of the biocideor antifouling agent is released from the capsule at room temperature to45° C. over 90 days and from which water or saltwater can leach thebiocide from the wall material, wherein the wall material contains adopant to enhance the diffusion of isothiazolone from the capsule and isa reaction product of polyvinyl alcohol, urea, resorcinol, andformaldehyde resin.
 2. The microencapsulated biocide of claim 1 whereinthe isothiazolone includes 4,5-dichloro-2-n-octyl-3(2H)-isothiazolone.3. The microencapsulated biocide of claim 2 wherein the isothiazolone ispresent in the core dissolved in a partially water soluble solvent. 4.The microencapsulated biocide of claim 1 wherein the dopant is polyvinylalcohol.
 5. The microencapsulated biocide of claim 3 wherein thepartially water soluble solvent dissolves in water in an amount of about0.5 to about 5% and is incorporated into the core in an amount of about5 to about 25%.
 6. The microencapsulated biocide of claim 5 wherein thesolvent is an ester or an ether or mixtures thereof.
 7. Themicroencapsulated biocide of claim 1 wherein the wall material is a dualwall microcapsule including a melamine-formaldehyde inner wall.
 8. Themicroencapsulated biocide of claim 1 wherein the dopant is selected fromthe group consisting of polyvinyl alcohol, hydroxylethylcellulose,hydroxypropylcellulose, methylcellulose, hydroxyethylmethylcellulose,hydroxypropylmethylcellulose, hyroxybutylmethylcellulose,ethylhydroxyethylcellulose, and polyethylene glycols.
 9. Themicroencapsulated biocide of claim 1 wherein the wall material is a dualwall having an inner wall and an outer wall.
 10. The microencapsulatedbiocide 9 wherein the inner wall includes is an acrylic polymer and theouter wall is a PVA-urea-resorcinol-formaldehyde(URF) polymer.
 11. Themicroencapsulated biocide of claim 9 wherein the inner wall is aninterfacial reaction product of an aromatic polyisocyanate and the outerwall is a PVA-urea-resorcinol-formaldehye(URF) condensation polymer. 12.The microencapsulated biocide of claim 9 wherein the inner wall is amelamine-formaldehyde and the outer wall is aPVA-urea-resorcinol-formaldehye(URF) polymer.